It has been demonstrated in young adults that aerobic exercise training enhances cardiac parasympathetic (or vagal) nerve activity. This improved vagal-cardiac function is cardioprotective. Recently, we found that a compromised arterial blood pressure (ABP) regulation in elderly adults was associated with an age-related vagal dysfunction. Since aging is accompanied by chronic physical inactivity, questions remain as to whether aerobic exercise training can reverse the vagal dysfunction manifest in the elderly. We hypothesize that elderly adults with greater relative aerobic capacity will have greater autonomic neural control of the heart than their age matched counterparts and that the enhanced vagal-cardiac modulation resulting from exercise training will assist in APB stability at rest and during orthostatic challenge. We will test these hypotheses by evaluating vagally mediated control of cardiac function and baroreflex control of blood pressure in trained and in untrained elderly subjects aged 65 - 75 years. Selective muscarinic and beta1-adrenergic blockade will be used to determine the effects of endurance training on the specific neural area of the autonomic neural control of the heart affected by exercise training. Additionally, the effect of exercise training will be assessed by comparing untrained elderly subjects before and after one year of moderate intensity aerobic exercise training. Our long-term objectives are to understand the albeit regulatory mechanisms of blood pressure and blood volume due to age and to provide the basis for the use of prophylactic measure to improve the quality of human life.